Because they aren't going to be alone doing this for very long. Competitors will just undercut each other until just above the cost threshold. And people will simply pick the one that gets them from A to B fast and cheap. I've never cared about who drives my Uber/Taxi, what car shows up, etc. It's just a service that I buy without knowing any of that. It's only a problem if they don't show up.

The cost threshold should be pretty low. No fuel (only electricity), and no drivers. Those are two of the larger cost factors here.